Thermal Modeling, Analysis, and Management in VLSI Circuits: Principles and Methods

The growing packing density and power consumption of very large scale integration (VLSI) circuits have made thermal effects one of the most important concerns of VLSI designers. The increasing variability of key process parameters in nanometer CMOS technologies has resulted in larger impact of the substrate and metal line temperatures on the reliability and performance of the devices and interconnections. Recent data shows that more than 50% of all integrated circuit failures are related to thermal issues. This paper presents a brief discussion of key sources of power dissipation and their temperature relation in CMOS VLSI circuits, and techniques for full-chip temperature calculation with special attention to its implications on the design of high-performance, low-power VLSI circuits. The paper is concluded with an overview of techniques to improve the full-chip thermal integrity by means of off-chip versus on-chip and static versus adaptive methods.     

Full-chip subthreshold leakage power prediction and reduction techniques for sub-0.18-/spl mu/m CMOS

The driving force for the semiconductor industry growth has been the elegant scaling nature of CMOS technology. In future CMOS technology generations, supply and threshold voltages will have to continually scale to sustain performance increase, control switching power dissipation, and maintain reliability. These continual scaling requirements on supply and threshold voltages pose several technology and circuit design challenges. With threshold voltage scaling, subthreshold leakage power is expected to become a significant portion of the total power in future CMOS systems. Therefore, it becomes crucial to predict and reduce subthreshold leakage power of such systems. In the first part of this paper, we present a subthreshold leakage power prediction model that takes into account within-die threshold voltage variation. Statistical measurements of 32-bit microprocessors in 0.18-/spl mu/m CMOS confirm that the mean error of the model is 4%. In the second part of this paper, we present the use of stacked devices to reduce system subthreshold leakage power without reducing system performance. A model to predict the scaling nature of this stack effect and verification of the model through statistical device measurements in 0.18-/spl mu/m and 0.13-/spl mu/m are presented. Measurements also demonstrate reduction in threshold voltage variation for stacked devices compared to nonstack devices. Comparison of the stack effect to the use of high threshold voltage or longer channel length devices for subthreshold leakage reduction is also discussed.     

INDEP approach for leakage reduction in nanoscale CMOS circuits

Complementary metal oxide semiconductor (CMOS) technology scaling for improving speed and functionality turns leakage power one of the major concerns for nanoscale circuits design. The minimization of leakage power is a rising challenge for the design of the existing and future nanoscale CMOS circuits. This paper presents a novel, input-dependent, transistor-level, low leakage and reliable INput DEPendent (INDEP) approach for nanoscale CMOS circuits. INDEP approach is based on Boolean logic calculations for the input signals of the extra inserted transistors within the logic circuit. The gate terminals of extra inserted transistors depend on the primary input combinations of the logic circuits. The appropriate selection of input gate voltages of INDEP transistors are reducing the leakage current efficiently along with rail to rail output voltage swing. The important characteristic of INDEP approach is that it works well in both active as well as standby modes of the circuits. This approach overcomes the limitations created by the prevalent current leakage reduction techniques. The simulation results indicate that INDEP approach mitigates 41.6% and 35% leakage power for 1-bit full adder and ISCAS-85 c17 benchmark circuit, respectively, at 32 nm bulk CMOS technology node.     

A minimum total power methodology for projecting limits on CMOS GSI

A circuit design methodology minimizing total power drain of a static complementary metal-oxide-semiconductor (CMOS) random logic network for a prescribed performance, operating temperature range, and short channel threshold voltage rolloff is investigated. Physical, continuous, smooth, and compact “transregional” MOSFET drain current models that consider high-field effects in scaled devices and permit tradeoffs between saturation drive current and subthreshold leakage current are employed to model CMOS circuit performance and power dissipation at low voltages. Transregional models are used in conjunction with physical short channel MOSFET threshold voltage rolloff models and stochastic interconnect distributions to project optimal supply voltages, threshold voltages, and device channel widths minimizing total power dissipated by CMOS logic circuits for each National Technology Roadmap for Semiconductors (NTRS) technology generation. Optimum supply voltage, corresponding to minimum total power dissipation, is projected to scale to 510 mV for the 50-nm 10-GHz CMOS generation in the year 2012. Techniques exploiting datapath parallelism to further scale the supply voltage are shown to offer decreasing reductions in power dissipation with technology scaling     

Leakage current mechanisms and leakage reduction techniques in deep-submicrometer CMOS circuits

High leakage current in deep-submicrometer regimes is becoming a significant contributor to power dissipation of CMOS circuits as threshold voltage, channel length, and gate oxide thickness are reduced. Consequently, the identification and modeling of different leakage components is very important for estimation and reduction of leakage power, especially for low-power applications. This paper reviews various transistor intrinsic leakage mechanisms, including weak inversion, drain-induced barrier lowering, gate-induced drain leakage, and gate oxide tunneling. Channel engineering techniques including retrograde well and halo doping are explained as means to manage short-channel effects for continuous scaling of CMOS devices. Finally, the paper explores different circuit techniques to reduce the leakage power consumption.     

Power dissipation sources and possible control techniques in ultra deep submicron CMOS technologies

As technology scales down into the ultra deep-submicron (UDSM) region, the static power dissipations grow exponentially and become an increasingly dominant component of the total power dissipation in CMOS circuits. With increase in gate leakage current resulting from thinner gate oxides in UDSM and the problems associated with short channel effects, leakage power dissipation is becoming a huge factor challenging a continuous success of CMOS technology in the semiconductor industry. With strict limitations of maximum allowable power (the power being limited more by system level cooling and test constraints than packaging) of 2.8 W (in 2005) to 3 W (in 2020) for battery (low cost/handheld) operated devices as projected by the International Technology Roadmap for Semiconductors (ITRS) 2005, innovations in leakage control and management are urgently needed. This paper presents an overview of the sources of the power dissipation mechanisms in the UDSM technologies, and the device and circuit techniques to control them.     

LECTOR: a technique for leakage reduction in CMOS circuits

In CMOS circuits, the reduction of the threshold voltage due to voltage scaling leads to increase in subthreshold leakage current and hence static power dissipation. We propose a novel technique called LECTOR for designing CMOS gates which significantly cuts down the leakage current without increasing the dynamic power dissipation. In the proposed technique, we introduce two leakage control transistors (a p-type and a n-type) within the logic gate for which the gate terminal of each leakage control transistor (LCT) is controlled by the source of the other. In this arrangement, one of the LCTs is always "near its cutoff voltage" for any input combination. This increases the resistance of the path from V/sub dd/ to ground, leading to significant decrease in leakage currents. The gate-level netlist of the given circuit is first converted into a static CMOS complex gate implementation and then LCTs are introduced to obtain a leakage-controlled circuit. The significant feature of LECTOR is that it works effectively in both active and idle states of the circuit, resulting in better leakage reduction compared to other techniques. Further, the proposed technique overcomes the limitations posed by other existing methods for leakage reduction. Experimental results indicate an average leakage reduction of 79.4% for MCNC'91 benchmark circuits.     

Nanoarchitectonics for Heterogeneous Integrated Nanosystems

Based on projections of the International Roadmap for Semiconductors (ITRS), the continued scaling of complementary metal-oxide semiconductor (CMOS) devices will face severe technical challenges. Among the most critical are power dissipation and device-level variabilities that will make circuit design very difficult. Potential device-level solutions that take advantage of new functional materials, self-assembly processes, low dissipation nanoscale devices, and architectures that aim in sustaining Moore's law beyond the ITRS are discussed in this paper. Two potential paths forward are clear at this point. One path is to continue increasing chip-scale functional throughput by looking at new functional materials at atomic and molecular levels for assembly into new low-power devices with different logic state variables that can better tolerate variabilities. Another distinct approach is to increase chip-scale functionality by exploiting the heterogeneous integration of materials, such as compound semiconductors on silicon as enabled by the unique features in nanoscale epitaxy and self-assembly on a common substrate. This paper will discuss some possible methods forward in maintaining scaled CMOS and going beyond the roadmap.     

The incredible shrinking transistor

The steady down-scaling of CMOS device dimensions has been the main stimulus to the growth of microelectronics and the computer industry over the past two decades. The more an IC is scaled, the higher becomes its packing density, the higher its circuit speed, and the lower its power dissipation. Today, after many generations of scaling, the smallest feature in a CMOS transistor is approaching atomic dimensions and off-state leakage current per transistor has been rising because thermal energy does not scale. So how much longer can CMOS scaling continue? As the integration level of ICs moves toward 100 million transistors in the next few years, key issues of transistor design must be reexamined for 0.10-0.13-μm generation technology. In previous CMOS generations, it was possible to disregard many parasitic components like off-state leakage and gate current. But in the not-so-distant future, these undesirables will grow rapidly as the fundamental limits imposed by thermodynamics and quantum mechanics close in on the technology. Fortunately the margins in today's devices will be enough to blunt the impact of such effects for perhaps a few generations. All the same, extracting the most performance while extending the limit of CMOS will require several elaborate schemes, including multiple threshold voltages, optimum two-dimensional nonuniform doping, and near atomic level control of gate oxide thickness and source-drain profile     

Impact of gate induced drain leakage on overall leakage ofsubmicrometer CMOS VLSI circuits

In this paper, the impact of gate induced drain leakage (GIDL) on the overall leakage of submicrometer VLSI circuits is studied. GIDL constitutes a serious constraint, with regards to off-state current, in scaled down complimentary metal-oxide-semiconductor (CMOS) devices for DRAM and/or EEPROM applications. Our research shows that the GIDL current is also a serious problem in scaled CMOS digital VLSI circuits. We present the experimental and simulation data of GIDL current as a function of 0.35-μm CMOS technology parameters and layout of CMOS standard cells. The obtained results show that a poorly designed standard cell library for VLSI application may result in extremely high leakage current and poor yield     

PVT variations aware low leakage INDEP approach for nanoscale CMOS circuits

Increasing in device parameter variations is the critical issue in very deep sub-micron regime due to continue scaling of the transistor dimensions. The overall performance yield of the logic circuit is diminished by raising leakage current and variability issues in scaled devices. In this article; we have proposed an approach called INDEP, based on Boolean logic calculation for the input signals of the extra inserted transistors between the pull-up and pull-down network of the CMOS logic. INDEP approach is not only reduces the leakage current but also mitigates the variability issues with minimum susceptible delay paths. Various process, voltage and temperature (PVT) variations are analyzed at 22 nm BSIM4 bulk CMOS PTM technology node for chain of 5-inverters using HSPICE tool. Several guidelines are provided to design the variability aware CMOS circuits in nanoscale regime by considering the leakage current variation. INDEP approach works effectively in both active as well as standby state of the circuit and keeping the modal performance characteristics of the CMOS gate. The electrical simulation results show that our proposed INDEP approach is less susceptible to PVT variations as compared to conventional circuit. The Monte-Carlo simulation results confirm that average INDEP leakage current reduction is 62.31% at ±20% PVT variations under 3σ Gaussian distribution for chain of 5-inverters.     

纳米集成电路静态功耗机理及低功耗设计技术

对当前纳米级低功耗设计中静态功耗的产生机理以及各种降低漏电流功耗的电路设计理论及其特点做详细的论述．以期为相关研究：设计人员提供有益参考。     

Low-power high-performance double-gate fully depleted SOI circuitdesign

Double-gate fully depleted (DGFD) SOI circuits are regarded as the next generation VLSI circuits. This paper investigates the impact of scaling on the demand and challenges of DGFD SOI circuit design for low power and high performance. We study how the added back-gate capacitance affects circuit power and performance; how to tradeoff the enhanced short-channel effect immunity with the added back-channel leakage; and how the coupling between the front- and back-gates affects circuit reliability. Our analyses over different technology generations using the MEDICI device simulator show that DGFD SOI circuits have significant advantages in driving high output load. DGFD SOI circuits also show excellent ability in controlling leakage current. However, for low output load, no gain is obtained for DGFD SOI circuits. Also, it is necessary to optimize the back-gate oxide thickness for best leakage control. Moreover, threshold variation may cause reliability problems for thin back-gate oxide DGFD SOI circuits operated at low supply voltage     

A multi coding technique to reduce transition activity in VLSI circuits

Advances in VLSI technology have enabled the implementation of complex digital circuits in a single chip, reducing system size and power consumption. In deep submicron low power CMOS VLSI design, the main cause of energy dissipation is charging and discharging of internal node capacitances due to transition activity. Transition activity is one of the major factors that also affect the dynamic power dissipation. This paper proposes power reduction analyzed through algorithm and logic circuit levels. In algorithm level the key aspect of reducing power dissipation is by minimizing transition activity and is achieved by introducing a data coding technique. So a novel multi coding technique is introduced to improve the efficiency of transition activity up to 52.3% on the bus lines, which will automatically reduce the dynamic power dissipation. In addition, 1 bit full adders are introduced in the Hamming distance estimator block, which reduces the device count. This coding method is implemented using Verilog HDL. The overall performance is analyzed by using Modelsim and Xilinx Tools. In total 38.2% power saving capability is achieved compared to other existing methods.     

Overview and Design of Mixed-Voltage I/O Buffers With Low-Voltage Thin-Oxide CMOS Transistors

Overview on the prior designs of the mixed-voltage I/O buffers is provided in this work. A new 2.5/5-V mixed-voltage I/O buffer realized with only thin gate-oxide devices is proposed. The new proposed mixed-voltage I/O buffer with simpler dynamic n-well bias circuit and gate-tracking circuit can prevent the undesired leakage current paths and the gate-oxide reliability problem, which occur in the conventional CMOS I/O buffer. The new mixed-voltage I/O buffer has been fabricated and verified in a 0.25-$mu$m CMOS process to serve 2.5/5-V I/O interface. Besides, another 2.5/5-V mixed-voltage I/O buffer without the subthreshold leakage problem for high-speed applications is also presented in this work. The speed, power consumption, area, and noise among these mixed-voltage I/O buffers are also compared and discussed. The new proposed mixed-voltage I/O buffers can be easily scaled toward 0.18-$mu$m (or below) CMOS processes to serve other mixed-voltage I/O interfaces, such as 1.8/3.3-V interface.     

冒险共振现象及其在CMOS电路最大功耗估计中的应用

随着集成电路工艺的不断提高，CMOS电路规模不断增大，功耗成为集成电路设计主要指标之一。文章首先以多位比较器为例，阐述了存在于部分多位电路功能块中的冒险共振现象；然后给出其在VLSI电路最大功耗估计中的应用。ISCAS85电路集实验结果证实了文章思路的有效性。     

A 90-nm CMOS Low-Power GSM/EDGE Multimedia-Enhanced Baseband Processor With 380-MHz ARM926 Core and Mixed-Signal Extensions

To meet the widely varying speed and power requirements of multifunctional mobile devices, an appropriate combination of technology features, circuit-level low-power techniques, and system architecture is implemented in a GSM/Edge baseband processor with multimedia and mixed-signal extensions. Power reduction techniques and performance requirements are derived from an analysis of relevant use cases and applications. The 44 mm² baseband processor is fabricated in a 90-nm low-power CMOS technology with triple-well option and dual-gate oxide core devices. The ARM926 core achieves a maximum clock frequency of 380 MHz at 1.4-V supply due to the usage of thin oxide (1.6 nm) devices. Power dissipation can be adapted to the performance requirements by means of combined voltage and frequency scaling to reduce active power consumption in medium-performance mode by 68%. To reduce leakage currents during standby mode, large SRAM blocks, nFET sleep transistors, and circuit components with relaxed performance requirements are implemented using devices with 2.2-nm gate oxide thickness     

低功耗CMOS逻辑电路设计综述

分析了ＣＭＯＳ逻辑电路的功耗来源从降低电源电压、减 上负载电容和逻辑电路开关活动几率等方面论述了降国耗的途径。讨论了深亚微米器件中亚同值电流对功耗的影响以及减小亚阈值电流的措施,最后分析了高层次设计对降低功耗的关键作用,说明低功耗设计必须从设计的各个层次加在考虑,实现整体优化设计。     

The impact of semiconductor technology scaling on CMOS RF and digital circuits for wireless application

The impact of CMOS technology scaling on the various radio frequency (RF) circuit components such as active, passive and digital circuits is presented. Firstly, the impact of technology scaling on the noise and linearity of the low-noise amplifier (LNA) is thoroughly analyzed. Then two new circuits, i.e., CMOS complementary parallel push-pull (CCPP) circuit and vertical-NPN (V-NPN) circuit for direct-conversion receiver (DCR), are introduced. In CCPP, the high RF performance of pMOS comparable to nMOS provides single ended differential RF signal processing capability without the use of a bulky balun. The use of parasitic V-NPN bipolar transistor, available in triple well CMOS technology, has shown to provide more than an order of magnitude improvement in 1/f noise and dc offset related problems, which have been the bottleneck for CMOS single chip integration. Then CMOS technology scaling for various passive device performances such as the inductor, varactor, MIM capacitor, and switched capacitor, is discussed. Both the forward scaling of the active devices and the inverse scaling of interconnection layer, i.e., more interconnection layers with effectively thicker total dielectric and metal layers, provide very favorable scenario for all passive devices. Finally, the impact of CMOS scaling on the various digital circuits is introduced, taking the digital modem blocks, the various digital calibration circuits, the switching RF power amplifier, and eventually the software defined radio, as examples.     

一种用于数字集成系统的新型CMOS三态缓冲器的设计

三态逻辑电路已被广泛应用于VLSI数字集成系统中.现在也有很多种实现三态逻辑的方法,但它们要么输出驱动能力不足够强要么占有较大的器件面积.在研究传统三态缓冲器的基础上设计了一种新型的三态缓冲器,据我们所知,这是使用晶体管数目最少的一种三态缓冲器结构.通过SPICE仿真实验表明,所设计的三态缓冲器与传统三态缓冲器相比具有更优的面积-延时积特性和更低的静态功耗.